1. Field of the Invention
This invention relates to the non-invasive measurement of moisture content of various materials. Electronic technicians have ordinary skill in this art.
2. Description of the Related Art
The related art is replete with devices for the noninvasive measurement of moisture content by use of electromagnetic waves. Although each application varies in its exact method of operation, for the most part each of the related art devices has a radio or microwave frequency signal generator which feeds an antenna. This antenna acts to transmit an electromagnetic wave through the specimen whose moisture content is to be measured. Opposite to, or otherwise in receiving relationship to, the transmission antenna is a receiving antenna. Between the two antennas in operational relationship is a specimen space wherein the specimen to be measured is placed during the measurement procedure.
The principle of operation of the related art devices is simply that an electromagnetic wave propagates through the specimen in question. The receiving antenna receives the electromagnetic wave and calculates an amount or percentage of water in the specimen based on any of a number of characteristics of the electromagnetic wave including signal strength, polarization, attenuation or absorption of the electromagnetic wave, phase angle or scattering of the electromagnetic wave.
The antennae of the related art devices are usually horn type directional wave guides, placed as close as possible to the specimen, that direct the propagating electromagnetic wave through a small or at least a particular portion of the specimen measured. If the transmitting horn cannot direct the propagating wave across the entire specimen at one time, an accurate reading of the moisture content in the overall specimen requires an average across the specimen.
The typical frequencies of electromagnetic waves used in the related art devices are in the microwave or radio frequency ranges. Using these high frequency electromagnetic waves creates a host of problems like: complex electric circuitry to create the high frequency signal; high frequency current amplification systems; impedance matching systems; matched polarization transmission and receiving antennae; superheterodyne receiving circuitry; and all the shielding necessary in such high frequency circuits to prevent unwanted noise and cross talk.
The related art devices measure the moisture content of specimens such as gypsum board, baled material including cotton, cotton and other materials as they fall within a chute, and other fibrous substances. The term cotton includes lint cotton, that is cotton already ginned or removed from the seed, and seed cotton, which has the cotton fibers still attached to the cotton seed.